return period

Return period is a statistical concept used to estimate how often a specific event, like a flood or heavy rain, is expected to occur. It’s usually expressed in years; for example, a "100-year flood" is an event that has a 1% chance of happening in any given year. It doesn’t mean it will only happen once every 100 years, but that, statistically, such an event is likely to occur once every century on average. The return period helps planners and engineers design structures and prepare for rare but significant events by understanding their likelihood over time.